1. Technical Field
The present invention relates generally to the field of semiconductor manufacturing and, more specifically, to a method for forming spacers on horizontal surfaces.
2. Background Art
The need to remain cost and performance competitive in the production of semiconductor devices has caused continually increasing device density in integrated circuits. To facilitate the increase in device density, new technologies are constantly needed to allow the feature size of these semiconductor devices to be reduced.
One of the bedrock technologies in semiconductor fabrication is the use of sidewall spacers. Typical sidewall spacers are formed using a conformal deposition of a spacer material over a structure, followed by a directional etch, as disclosed in Pogge, U.S. Pat. No. 4,256,514, "Method for Forming a Narrow Dimensioned Region on a Body," assigned to International Business Machines, Inc. The directional etch removes all the spacer material from the horizontal surfaces, but leaves "spacers" on the vertical surfaces of the structure. To form sidewall spacers material is conformally deposited over the structure, covering the horizontal and vertical surfaces. A directional etch is then preformed. This directional etch removes the material from the horizontal surfaces, while leaving the material on the sidewalls to form sidewall spacers. These spacers are inherently self-aligned with the sidewalls. These sidewall spacers can be used in a wide variety of applications for a wide variety of reasons For example, the use of sidewall spacers has been particular useful in the formation of field effect transistors (FETs). In this application sidewall spacers are formed on the sidewalls of transistor gates, where they are used to protect the gates and allow for improved dopant control at the gate edges.
Unfortunately, the sidewall spacers has several limitations. The most significant limitation is that sidewall spacers, as their name implies, can only be formed on the vertical surfaces or sidewalls of the structure. There is no corresponding simple way to form an inherently self aligned spacer on the horizontal surface while removing all the spacer material from the vertical surfaces. Such a horizontal surface spacer could be used in a wide variety of applications, such as whenever selective processing needs to be done to the vertical surfaces while the horizontal surfaces remain protected.
Thus, there is exists a need for a self-aligned spacer design that covers horizontal surfaces while being removed from vertical surfaces.